High power RF and microwave devices are generally implemented as hybrid devices. These hybrid devices typically include one or more transistor chips, one or more capacitor chips, and one or more inductors that are housed in a package. The one or more capacitor chips are typically realized using silicon metal oxide semiconductor (MOS), silicon metal insulator metal (MIM), or ceramic MIM components. The one or more inductors are typically realized using wirebonds.
These hybrid devices typically incorporate one or more input matching sections coupled to the input of one or more transistors, and one or more output matching sections coupled to the output of the one or more transistors. Usually, the first output matching section (e.g., the section directly coupled or closest to the transistor) is typically situated within the hybrid package due to the relatively low impedance created by the paralleling of many power transistor cells.
Generally, the output modeling of these high power devices typically include a resistor in parallel with a capacitor. In the past, the first output matching section typically consists of a shunt inductor adapted to resonate with the output capacitance of the active device at or near the operating frequency. This is better illustrated and explained with reference to the following example.
FIG. 1A illustrates a schematic diagram of a conventional high power RF/microwave circuit 100. In this example, the high power RF/microwave circuit 100 includes a bipolar junction transistor (BJT) as the active power device of the high power RF/microwave circuit 100. The high power RF/microwave circuit 100 also includes an input matching network having a first input series inductor LIN1, an input shunt capacitor CIN, a second input series inductor LIN2, and an input base inductor LBIN. The high power RF/microwave circuit 100 further includes an output matching network having an output series inductor LC1, a shunt inductor LSH1, a DC block capacitor CDC, and an output base inductor LBOUT. It is the shunt inductor LSH1 that is configured to resonate with the output capacitance of the BJT at or near the operating frequency of the high power RF/microwave circuit 100.
FIGS. 1B-1C illustrate top and side views of an actual implementation of the conventional high power RF/microwave circuit 100. As seen, the inductors are realized as wirebonds. For instance, the first input series inductor LIN1 is realized as a first set of parallel wirebonds connected at one end to an input metallization pad and at another end to a bridge, and a second set of parallel wirebonds connected at one end to the bridge and at another end to the non-ground terminal of the input capacitor CIN. The second input series inductor LIN2 is realized as another set of parallel wirebonds connected at one end to the non-grounded terminal of capacitor CIN and to the emitter of the BJT. The input base inductor LBIN is realized as a set of parallel wirebonds connected at one end to the grounded terminal of the input capacitor CIN and to the base of the BJT. The capacitor CIN and the bridge are disposed on a grounded metallization pad formed on a dielectric substrate MS1. As previously discussed, the inductors LIN1, LIN2, and LBIN, and capacitor CIN form at least part of the input matching network of the high power RF/microwave circuit 100.
With regard to the output matching network of the high power RF/microwave circuit 100, the output base inductor LBOUT is realized as a set of parallel wirebonds connected at one end to the base of the BJT and to the grounded terminal of the DC block capacitor CDC. The output series inductor LC1 is realized as a set of parallel wirebonds connected at one end to a “collector” metallization pad that is electrically connected to the collector of the BJT and at another end to an output metallization pad. The shunt inductor is realized as a set of parallel wirebonds connected at one end to the “collector” metallization pad and to the non-grounded terminal of the DC block capacitor CDC. The DC block capacitor CDC is disposed on a grounded metallization pad, which is formed on the dielectric substrate MS1.
As seen best in FIG. 1B, because both the shunt inductor wirebond LSH1 and the output series inductor wirebond LC1 are connected at one end to the “collector” metallization pad and both extend parallel towards the output metallization pad at similar heights, a shunt inductor wirebond LSH1 occupies the space that would otherwise be occupied by a series inductor wirebond LC1. Thus, this puts a limit on the number of shunt inductor wirebonds that can be provided, and also requires a sacrifice of a series inductor wirebond for each added shunt inductor wirebond. This has adverse consequences on the performance of the conventional high power RF/microwave circuit 100.
For instance, the less number of output series inductor wirebonds causes the series inductance and resistance to be higher. This has the adverse effect of lowering the operating bandwidth of the high power RF/microwave circuit 100 due to the higher output series inductance, since the bandwidth is inversely proportional to the square-root of the output series inductance. This also has the adverse effect of more power losses at the output due to the higher output series resistance, which reduces the power efficiency and gain of the high power RF/microwave circuit 100.
Additionally, the less number of shunt inductor wirebonds produces a higher resistance to ground. This additionally produces more power losses at the output, which results in lower power efficiency and gain. Further, as illustrated in FIG. 1B, because a relatively small number of shunt inductor wirebonds are provided for numerous fingers of the BJT (e.g., 2 wirebonds per 200 fingers), the load distribution across the BJT varies substantially. This results in elevated temperatures at regions where there is an absence of a wirebond. This results in a lower life for the BJT. In addition, the uneven load distribution also reduces the load mismatch tolerance (LMT) because of high VSWR peaks at regions where there is an absence of a wirebond.